A new species of the genus Ptychognathus Stimpson, 1858 (Crustacea: Brachyura: Varunidae) from Vanuatu.

Ptychognathus Stimpson, 1858 is a speciose genus in the family Varunidae, widely distributed in the Indo-West Pacific. Although species of Ptychognathus are common in estuaries with low salinity, some species are difficult to be identified correctly because of their small body size and similar morphology. This study describes one new species, Ptychognathus amikee sp. nov., from Vanuatu based on the morphological differences and the genetic data from mitochondrial cytochrome c oxidase subunit 1 (COI). This new species can be distinguished from the other congeners by the characters of the carapace, male chelipeds, and ambulatory legs.